Abstract: The present invention is directed generally to an apparatus and methods that combine a novel four-port dual-source interferometer with double modulation FT-VCD or FT-VLD measurements to obtain a spectrometer with enhanced signal quality (S/N), and lower susceptibility to detector saturation. In the novel apparatus of the present invention, a linear polarizer or tandem array of identically-oriented polarizers is placed in front of each of the two sources in a four-port dual-source interferometer, with the polarization state of one of the linear polarizers (or tandem array of polarizers) vertical and the polarization state of the other linear polarizer (or tandem array of polarizers) horizontal, i.e., with the polarization axes of the polarizers orthogonal to one another. Methods for measuring these spectra using the various aspects of the apparatus of the present invention are also provided.

Abstract: A method and apparatus to monitor the enantiomeric excess of chiral molecules participating in a chemical reaction. The method includes real time monitoring of the chemical reaction by obtaining a VCD spectra and an IR spectra of the chemical compounds in the reaction, and manipulating the spectra to obtain a % EE value. Using such real time information, the reaction parameters can be changed to shift the reaction to produce more of one chiral molecule than another.

Abstract: The invention describes a method to eliminate instrumental offset in measurement of optically active scattering and circular dichroism. The method uses the time-average measurement of the light that is systematically transformed by a series of optical devices. The optical devises perform the function of rotating linearly polarized light, interconverting left and right circular polarized light, converting circular polarized light to rotating linear polarized light and converting linear polarized light to alternating left and right circular polarized light.

Abstract: The invention describes a method to eliminate instrumental offset in measurement of optically active scattering and circular dichroism. The method uses the time-average measurement of the light that is systematically transformed by a series of optical devices. The optical devises perform the function of rotating linearly polarized light, interconverting left and right circular polarized light, converting circular polarized light to rotating linear polarized light and converting linear polarized light to alternating left and right circular polarized light.

Abstract: A circular dichroism spectrometer eliminates linear birefringent interference by having a first polarization modulator before the sample and a second polarzation modulator after the sample. The two polarization modulators vibrate at different frequencies so the signals can be distinguished and manipulated. The addition of the second polarization modulator, an additional lock in amplifier, and software to manipulate the two signals corresponding to the two vibrational frequencies allow a real time circular dichroism spectra free from interference to be determined.